The present invention is related to vehicle service systems, and in particular, to vehicle service systems such as vehicle wheel alignment systems, which are configured to acquire measurements of tire pressure for a wheel assembly of a vehicle undergoing a service procedure directly and from a tire pressure monitoring system sensor, and to utilize the acquired tire pressure measurements during a vehicle service procedure, such as to carry out diagnostic evaluation of the tire pressure monitoring system.
Modern vehicle wheel assemblies on most motor vehicles today consist of a pneumatic tire mounted or seated on a wheel rim, such as shown in FIG. 1. The tire is secured to the wheel rim by forces exerted between the inner peripheral edges of the tire, i.e. the beads, and the mating surfaces of the wheel rim, i.e. the bead seats. Pressurized air contained within the toroidal volume defined between the tire and wheel rim supports the tire against the weight of the vehicle. Tire pressure monitoring systems associated with motor vehicles such as passenger cars and light trucks are designed to provide a warning to drivers if the pressure level of air within tire on the vehicle becomes significantly decreased during operation. There are two types of tire pressure monitoring systems currently in use. The first is an indirect system, which relies upon rotational speed measurements acquired by the vehicle anti-lock braking system sensors during vehicle operation. A tire which is significantly deflated relative to the remaining tires on the vehicle will have a smaller rolling radius, and therefore will rotate faster. Significant differences in vehicle wheel rotational speeds are interpreted as being indicative of an under-inflated tire by an indirect tire pressure monitoring system, and a suitable warning is provided to the vehicle operator. However, indirect tire pressure monitoring systems cannot identify small changes in tire pressures, and are incapable of identifying situations in which all of the vehicle wheels are under-inflated.
The second type of tire pressure monitoring system is a “direct” system, in which each wheel assembly of the vehicle is equipped with a tire pressure sensor disposed in an operative relationship to the pressurize air contained between the tire and wheel rim. For example, as is shown in FIG. 2, a tire pressure sensor may be strapped about the surface of the vehicle wheel rim, such that the tire pressure sensor is disposed within the volume defined by the tire about the wheel rim. Alternatively, as shown in FIG. 3, the tire pressure sensors may be coupled to, or associated with, the valve stem of the vehicle wheel assembly. Typically, tire pressure sensors are configured to transmit data using high-frequency radio waves in the preferred range of 300 MHz-450 MHz to a common control unit. Specific frequencies such as 303 MHz, 315 MHz, 418 MHz, 434 MHz, and optionally 868 MHz are generally employed by tire pressure monitoring systems currently in use. The common control unit is configured to process the received data and provide the operator with a suitable display of vehicle wheel tire pressures. An exemplary “direct” tire pressure monitoring system is manufactured and sold by Smartire Systems, Inc. of Richmond, Calif. These “direct” tire pressure monitoring systems, which are semi-permanently installed, should not be confused with the process of acquiring “direct” measurements of the pressure in a tire such as by manual or automatic use of an external tire pressure gauge temporarily coupled to the tire valve stem and removed after use.
To prevent cross-talk between tire pressure monitoring systems of nearby vehicles, each tire pressure sensor is configured to transmit a unique identification code together with the tire pressure data signal. Depending upon the configuration of the particular “direct” system, and the signal range, the tire pressure monitoring system may be utilized to further monitor pressure in a vehicle's spare tire, or pressure in the tires of a towed trailer.
To provide a vehicle operator with useful information regarding tire pressure levels, a “direct” tire pressure monitoring system must provide the operator with a means to identify which monitored tires have reduced tire pressure. Identifying the vehicle wheel location for each tire pressure sensor in a vehicle tire pressure monitoring system may be done manually or automatically. Manual systems require some form of operator interaction, such as by physically installing predetermined tire pressure sensors in tires positioned in predetermined locations about a vehicle. Alternatively, each tire pressure sensor can be identified by a unique indicator to the common control unit, for example, a color-coded marking on the tire valve stem. When a low tire pressure condition is detected by one of the tire pressure sensors, the control unit displays a corresponding color to the vehicle operator, requiring the operator to inspect the vehicle wheels to located the corresponding color marking. Manual systems often require the operator to retrain or reposition the tire pressure sensors following a vehicle wheel rotation or service, a time-consuming and error-prone procedure.
Alternatively, tire pressure monitoring systems may be configured to automatically identify the corresponding tire locations associated with each tire pressure sensor in the system. These “automatic” systems typically provide a trigger mechanism or signal to activate each tire pressure sensor's transmitter in a predetermined sequence. The unique identification associated with each transmitter is stored as it is received in the predetermined sequence, thereby associating each tire pressure sensor with a known tire location. For some systems, the tire pressure sensors include a magnetic switch which is activated or triggered by the proximity of a magnetic field to direct the tire pressure sensor to transmit the unique identification. Alternate systems incorporate a radio-frequency receiver into each of the tire pressure sensors. Each of the receivers responds to a specific trigger signal, typically around 125 MHz, to transmit the associated tire pressure sensor's unique identification. While the programming of an “automatic” system remains time consuming, the need to physically reposition each tire pressure sensor following a tire rotation or tire service is eliminated, saving significant time during a vehicle service procedure.
Still other tire pressure monitoring systems are fully automatic in terms of locating each of the tire pressure sensors associated with a vehicle. These systems typically employed radio-frequency antenna disposed in proximity to the vehicle wheels, and uniquely identify each individual tire pressure sensor by monitoring the strength of the signals emitted by each tire pressure sensor, specific antenna identification codes, or specific radio-frequency variations on the order of a few KHz, associated with each tire pressure sensor.
Measurements of tire pressure in the individual wheel assemblies of a vehicle undergoing a vehicle service procedure may be useful in determining vehicle measurements and/or the proper operation of a vehicle-mounted tire pressure monitoring system. Accordingly, it would be advantageous to provide a vehicle service system, such as a vehicle wheel alignment system, with the necessary functionality to acquire measurements of tire pressure for one or more wheels of a vehicle undergoing a vehicle service procedure. Additional benefit may be obtained by providing the vehicle service system with the necessary functionality to access stored data representative of tire pressure specifications associated with the wheel assemblies of a vehicle. This stored data may, for example, be stored in an accessible database, in a vehicle on-board control unit, or in a data storage device associated with the individual vehicle wheel assemblies.
It would further be advantageous to provide a vehicle service system, such as a vehicle wheel alignment system or a stand-alone tire service system, with the necessary functionality to detect the presence of an installed tire pressure monitoring system (TPMS) on a vehicle undergoing a vehicle service procedure, and to receive signals from the tire pressure monitoring system which are indicative of tire pressure and/or temperature measurements.
It would be further advantageous for a vehicle service system, such as a vehicle wheel alignment system, to carry out diagnostic and calibration functions associated with an installed tire pressure monitoring system (TPMS) on a vehicle undergoing a vehicle service procedure.
It would be further advantageous to provide an integrated vehicle service system that includes all items necessary to completely diagnose a complex TPMS/Tire Pressure system. Previous systems involved stand-alone hand-held tools or OEM scan tools and many manual tasks that could introduce errors or misinterpretations. A technician had to be specially trained how to use each hand-held tool and each OEM scan tool, and the nuances associated with each. Previous procedures often included removing the wheels before the TPMS system is checked, leading to customer complaints that the service shop damaged the TPMS devices. The various alternate embodiments of the present invention provide a vehicle service system which is configured for acquiring direct tire pressure measurements and for communication with the ECU of a vehicle to test the functionality and operation of the entire TPMS system of the vehicle. Previous hand-held systems do not typically check the ECU functionality in that system, but only the individual TPMS devices. Current procedures are labor intensive, cumbersome, and error-prone due to the limitations mentioned above.